Catalyst comprising dispersed alkali metal and alkali metal mercaptide and polymerization process employing said catalyst



Patented Oct. 4, 1949 CATALYST COMPRISING DISPERSED ALKALI METAL ANDALKALI METAL MERCAPTIDE AND POLYMERIZATION PROCESS EM- PLOYING SAIDCATALYST Willie W. Crouch, Bartlesville, kla., asalgnor to PhillipsPetroleum Company, a corporation of Delaware No Drawing. Application May23, 1946, Serial No. 671,900

18 Claims. 1

The present invention relates to a process and catalyst for thepolymerization of polymerizable organic compounds. In one of its morespecific aspects it relates to a process for the mass polymerization ofa conjugated diolefin and to the improved product produced thereby.Another aspect of the invention is the method of preparation of acatalyst for the polymerization of poly. merizable organic compounds andthe improved polymerization catalyst so prepared. In one of its morespecific aspects this invention relates to the mass copolymerization ofbutadiene and styrene using an improved alkali metal contact catalystand to the improved product produced by this process.

The present invention provides a process especially suited for the masspolymerization of polymerizable organic compounds catalyzed by an alkalimetal. It also provides improved alkali metal catalysts in the form ofstable suspensions of the alkali metal in a suitable dispersing mediumwith the metal in an extremely fine state of division. Thepolymerization process forming part of the present invention isparticularly adapted to mass copolymerization of butadiene and styrenemonomers to form rubber-like elastomers. A stable suspension of analkali metal prepared by the method disclosed herein is used as acatalyst for the polymerization reaction. The method of preparation ofthe catalyst, which is also a part of the present invention, involvesthe use of a se lected surface active agent to accomplishthe suspensionof the alkali metal in a finely divided form.

Mass polymerization of conjugated diolefins, especially of1,3-butadiene, isoprene and 2,3-dimethyl butadiene has long been knownto be capable of resulting in high polymers or synthetic elastomershaving high elasticity and resembling natural gum rubber. While thereaction is essentially one of thermopolymerization it has been foundthat alkali metals, particularly sodium and potassium, accelerate thereaction markedly. In spite of the demand for improved syntheticelastomers, the difficulties attendant upon this type of polymerizationhave made it unattractive and have retarded commercial development ofthe process. One of the major problems which has confronted thedevelopment of mass polymerization has been the dissipation of the heatof polymerization. If this heat is not dissipated rapidly polymers ofpoor quality are produced and, in addition, charring of the product,serious explosions, fires, etc., are likely to occur. Failure to solvethese important technical problems directed emphasis to polymerizationin aqueous emulsions of the monomers. It is obvious that alkali metalcatalysts are inapplicable in aqueous emulsion polymerization systemsand, therefore, it has been 2 necessary to resort to other means forinitiating the reaction.

Even though the emulsion polymerization process has been developed andis used widely on a commercial scale, the elastomers produced possesscertain properties which render them inferior to natural rubber for manyuses. One property which is the most detrimental is that of heating inuse, the so-called hysteresis temperature rise, which is pronounced forthis type of polymer. The balance between this property and the numberof fiexures possible before the sample fails ("flex life) is still oneimportant area in which emulsion polymers are notably deficient.

An object of the present invention is to provide a novel process for thepolymerization of polymerizable organic compounds. Another object of thepresent invention is to provide a novel process for the polymerizationof organic materials using an alkali metal as a catalyst. A morespecific object is to provide such a process which is particularlysuited to the mass copolymerization of butadiene and styrene using adispersion of a comminuted alkali metal as catalyst. Another object ofthe present invention is to provide an improved alkali metal catalystfor polymerization reactions. Still another object is to provide animproved method for the preparation'of a stable suspension of finelydivided alkali metal in a suitable dispersing medium. Still anotherobject of the present invention is to provide an improved polymer orelastomer prepared by the polymerization process of this invention.

I have now found that mass polymerization of conjugated diolefins may becarried out successfully on an industrial scale, in the presence ofcatalysts consisting of stable suspensions of alkali metals, to producepolymers which have particularly good properties and are of uniformquality. In a copending application of W. A. Schulze and J. C. Hillyer,Serial No. 677,354, filed June 17, 1946, there is described a continuousprocess whereby the mass polymerization of conjugated diolefins may beadvantageously accomplished. The present process relates to anothermethod for eflfecting this polymerization of diolefins in the presenceof finely divided, metal catalysts prepared by dispersing the metal in adispersing medium in the presence of selected surface active agents.Through the application of the catalysts of this invention the drawbacksand operational dimculties of previous processes are almost completelyeliminated.

By the process of this invention polymers of remarkable uniformity andsuperior properties may be prepared, with greater ease and much saferoperation than has heretofore been possible, through the use of finelydivided metal catalysts, for example, sodium, said catalysts beingemployed in the form of stable suspensions and prepared in the presenceof surface active agents, for example, mercaptides of alkali metals.Heretofore mass polymerizations with alkali metal catalysts,particularly those polymerizations involving the use of simple diolefinmonomers, have generally been unsuccessful primarily on account ofdifficulties inherent in the catalysts. When sodium is employed in theform of chunks, or even fine wire or ribbon, the polymers which resultare hard. This hardness is particularly noticeable near the sodiumsurface. At the same time much of the remaining butadiene polymerizesonly to a very soft, sticky, semi-liquid material. Iron rods coated withsodium or potassium are likewise unsatisfactory as are any methods whichdo not produce the catalyst in finely divided form. The operationaldifiiculties which arise when these forms of alkali metal catalysts areemployed are numerous and the nonuniformity of the polymers makes suchprocesses of little value in commercial operations. n the other hand,when alkali metal catalysts are prepared in such a way as to present alarge surface area and the process operated to insure intimate contactof catalyst and reactants, polymers possessing superior properties aswell as uniform quality are obtained.

When operating with metal catalysts it is necessary to maintain a finestate of dispersion of catalyst with reactants. By vigorous agitation,the reactants may be kept in a fairly homogeneous state at the beginningof the polymerization but as the reaction proceeds the mixture becomesviscous and the catalyst tends to collect toward the bottom of thereaction zone. As a result of this settling out of the catalyst,polymerization is accelerated in certain areas and is finally localizedin regions of relatively high catalyst concentration thus causingoverheating and nonhomogeneity of the polymer. In the present processthese difiiculties are overcome by preparing the catalyst by a specialmethod, namely, by comminuting the alkali metal in a dispersing mediumusing a surface active agent, particularly a mercaptide-of an alkalimetal. By this method a very finely divided, stable suspension of themetal is obtained and intimate contact of the catalyst and the reactantsis insured throughout the operation.

The use of surface active agents in the preparation of suspensions ofalkali metal catalysts promotes the formation of catalyst particles ofuniform size. lowed for the preparation of catalysts of this type, thatis, without the use of surface active agents, the particles which resultshow appreciable variation in size with a considerable proportion ofthem being relatively large. It is a well established fact that only thesurface of the catalytic material promotes active polymerization. It is,therefore, obvious that large particles have a relatively high mass ofmetal per unit of active surface and, when these catalysts are employedin large scale commercial operations, an economic factor of considerableimportance is introduced. When large catalyst particles are present,there is also the increased difficulty and expense of destroying andremoving all the metal from the finished polymer. The large particlesare slow to react and excessive quantities of the reagent, such asmethanol, are required.

In one specific embodiment the present process comprises thecopolymerization of butadiene and When the general procedure isfolcharge to the reactor.

styrene in thepresence of a suspension of very finely divided metallicsodium as catalyst. A dispersion medium for the catalyst, e. g., xylene,previously dried and purified by distillation, is charged to a suitablevessel equipped with a high speed stirrer where it is heated to about210 F. or higher in an atmosphere of dried oxygen-free nitrogen. Freshlycut sodium is then charged to the vessel after which a selectedmercaptan, e. g., tertiary dodecyl mercaptan, is added in sufiicientamount to give a quantity of sodium mercaptide equivalent to about 0.5to 5.0 per cent of the weight of the sodium use. The temperature isadjusted to about 230 F. while the mixture is vigorously agitated bystirring at high speed (5,000 to 10,000 R. P. M.) from about 5 to aboutminutes or until a stable dispersion is obtained. The system is allowedto cool to about 210 F. and agitation is stopped.

Copolymerization of butadiene and styrene is carried out using theconventional proportions of butadiene ('75 parts) and styrene (25parts). The reaction is accomplished in the presence of a minor quantityof the catalyst suspension, for example, 0.1 to 0.5 per cent of thetotal monomer weight being sodium, and the mixture agitated v while thetemperature is held Within the range of about to F. Based on the monomercharge, from about 0.0005 to about 0.025 weight per cent sodiummercaptide is present in the The sodium catalyst is first introducedinto the reactor after which a portion of the butadiene is charged,followed by the styrene and then theremainder of the butadiene. At thecompletion of the reaction the polymer is removed by conventional means,such as by solution of the polymer in benzene followed by precipitationwith methanol, or the sodium may be destroyed by washing with water on awash mill. The polymers thus formed are of uniform quality and possessproperties superior to polymers obtained by other methods.

The metals applicable for the preparation of the catalysts of thisinvention are the alkali metals. For economic reasons sodium andpotassium are most generally used with sodium usually preferred. In thecatalyst preparation a dispersion is formed containing from about 5 toabout 35 weight per cent of the alkali metal, and preferably from about10 to about 20 weight per cent of the alkali metal. Using from 0.5 to 5per cent by Weight mercaptide (based on the weight of the sodium) thedispersion contains from about 0.025 to about 1.75 weight per centmercaptide.

The dispersing agents which may be employed for the preparation of thecatalyst suspensions described herein are toluene, xylene, mineral oil,paraffin wax and many other inert materials with boiling pointssufliciently high for satisfactory operation of the process. Whentemperatures of about 210 to 230 F. are employed, xylene is oftenpreferred as the dispersing material.

The catalyst dispersion stabilizers employed in this invention aremercaptides of alkali metals;

The mercaptides may be prepared from mercaptans containing from about toeight to about twenty carbon atoms with those containing from such asthose described herein, it is often considered desirable to use adiluent. Among the materialsapplicable for this purpose are isobutaneand higher boiling paramnic hydrocarbons, for example, n-butane,n-pentane and nheptane, cycloparafiins, e. g., cyclohexane, and aromatichydrocarbons, e. g., benzene.

It ishereinbefore stated that particle size is an important factor inthe satisfactory operation of this invention. When ordinary methods ofcatalyst preparation are employed, such as shaking a, heated mixture ofmetal and dispersing agent, the average particle size is often about 0.1to 0.2 mm. These particles settle out rapidly thus rendering thecatalyst ineffective for the production of a homogeneous polymer. Whenhigh speed stirrin methods are employed, it is possible to produce muchmore effective dispersion of the metal but there still remains thedisadvantage of coalescence of the particles when stirring is stopped.According to the method of my invention the addition of a dispersionstabilizer, e. g., a sodium mercaptide, to the mixture of dispersingmedium and metal, followed by high speed stirrin produces a catalyst ofparticle size ranging from about 0.01 to 0.02 mm. which does not undergocoalescence upon standing. In addition to producing very small particlesof metal, the present method yields stable catalyst suspensions whichnot only greatly accelerate mass polymerization reactions but also givepolymers possessing the desired characteristics. The extremely smallparticle size is particularly advantageous since it makes possible moreefi'ective contact between catalyst and reactants and also afiords amethod of bringing about the polymerization reactions with a muchsmaller.

' quantity of catalyst than is ordinarily required.

The polymers prepared through the use of the catalysts of this inventionhave particularly desirable properties, especially hysteresis-flex lifebalance. Not only do samples of the polymers excel in these propertiesbut they also have other characteristics equal to or better than thosepossessed by polymers obtained by other methods.

Example I A finely divided sodium catalyst was prepared in the followingmanner: 160 grams of dry'toluene, 16 grams of sodium and 0.32 gramtertiary dodecyl mercaptan were charged to a 500 ml. creased, roundflask equipped with a finned metal stirrer and the contents heated to230 F. and stirred at the rate of 9,000 to 10,000 R. P. M. for twentyminutes. The system was allowed to cool to 210 F. after which stirringwas discontinued. The preparation of the catalyst was carried out in Tan atmosphere of nitrogen to prevent oxidation of the sodium. Theaverage particle size of the catalystwas about 0.02 mm.

To a pressure autoclave containing the catalyst, styrene was chargedfollowed by butadiene and the polymerization was carried out over an8.5- hour period at a temperature of 85 F. with continuous agitation.The reactants used were in the ratio of 0.3 part sodium, 25 partsstyrene and 75 parts butadiene. At the conclusion of the reaction thepolymer was dissolved in benzene and precipitated by the addition ofmethanol. Two parallel runs gave intrinsic viscosities of 2.43 and 2.59,respectively. No gel was formed and a polymer of uniform quality wasobtained.

In contrast to the results obtained with a catalyst prepared usingtertiary dodecyl mercaptan as a suspension stabilizer, a catalyst waspre pared in a similar manner, but using no mercaptan. The size of thecatalyst particles varied from 0.02 to 0.1 mm. The polymer had anintrinsic viscosity of 4.85 and contained 7.3 per cent gel. Examinationof the product revealed a very noticeable lack of uniformity.

Example I! A catalyst was prepared as in Example I using A masspolymerization reaction was eflfected over a seven-hour period using acatalyst prepared from grams xylene, 32 grams. sodium and 0.64 gramtertiary dodecyl mercaptan. The size of the catalyst particles was 0.01to 0.02 mm. The polymerization recipe and procedure used in Example Iwere followed. Two reactions carried out simultaneously showed only atrace of gel and gave values of 3.01 and 3.30 for the intrinsicviscosity.

Since certain-changes may be made in carrying out the above processwithout departing from the scope of the invention, it is intended thatall matter contained in the foregoing description of the invention shallbe interpreted as illustrative and not in a limiting sense.

I claim: I

1. A process for the polymerization of a conjugated diolefin whichcomprises admixing said diolefin with a liquid inert hydrocarbondispersion containing a finely divided and dispersed alkali metal in anamount equivalent to from about 0.1 to about 0.5 weight per cent of saiddiolefin and a mercaptide of said alkali metal in an amount equivalentto from about 0.5 to about 5.0 weight per cent of the alkali metal.

2. In a process for the polymerization of butadiene in the presence offinely dispersed metallic sodium as a catalyst, the improvement which,

comprises carrying out the polymerization reaction in the presence of asodium mercaptide in an amount equivalent to from about 0.5 to about 5.0weight per cent of the sodium employed.

3. A process for the copolymerization of butadiene and styrene whichcomprises admixing said butadiene and styrene and incorporatingtherewith from about 0.1 to about 0.5 weight per cent comminuted sodiumand from about 0.0005 to about 0.025 weight per cent of sodiummercaptide in a dispersion in a liquid inert hydrocarbon.

4. A process for the preparation of a copolymer of 1,3-butadiene andstyrene which comprises polymerizing in admixture about 75 parts byweight. 1,3-butadiene and 25 parts by weight styrene and incorporatingtherewith in a liquid inert hydrocarbon dispersion from about 0.1 toabout 0.5 weight per cent sodium and from about 0.0005 to about 0.025weight per cent of a sodium mercaptide, and continuously agitating theresulting mixture at a temperature within the range of from about 80 toabout 125 F. until the polymerization reaction is substantiallycomplete.

5. In a process for the production of a copolymer of butadiene andstyrene in the presence of finely divided and dispersed metallic sodiumas a catalyst, the improvement which comprises carrying out thepolymerization reaction in the presence of a sodium mercaptidecontaining from about 8 to about 20 carbon atoms per molecule in anamount equivalent to 0.5 to 5.0 weight per cent of the sodium employed.

6. In a process for the preparation of a copolymer of butadiene andstyrene in the presence of finely divided and dispersed metallic sodiumas a catalyst, the improvement which comprises carrying out the,reaction in the presence of a sodium mercaptide prepared by theinteraction of metallic sodium with a tertiary alkyl mercaptancontaining'from 12 to 16 carbon atoms per molecule in an amountequivalent to from about 0.5 to about 5.0 weight per cent of the sodiumemployed.

7. A method for the preparation of a finely divided dispersion of analkali metal in a liquid inert hydrocarbon which comprises comminutingsaid alkali metal in said hydrocarbon in the presence'oi a mercaptide ofsaid alkali metal.

8. A method for the preparation of a dispersion of an alkali metal in aliquid inert hydrocarbon which comprises comminuating said alkali metalin said hydrocarbon in the presence of from about 0.5 to about 5.0weight per cent of a mercaptide of said metal containing from about 8 toabout 20 carbon atoms permolecule.

9. A method for the preparation of a dispersion of metallic sodium in aliquid inert aromatic hydrocarbon which comprises comminuting metallicsodium in said hydrocarbon in the presence of from about 0.5 to about5.0 weight per cent of a sodium mercaptide having from about 8 to about20 carbon atoms per molecule.

10. A method for the preparation of a dispersion of metallic sodium inxylene which comprises adding from about 5 to about 35 weight per centmetallic sodium to liquid xylene and comminuting the metallic sodium inthe xylene by vigorous agitation at a temperature within the range offrom about 210 to about 230 F. and in the presence of from about 0.5 toabout 5 weight per cent based on the sodium of a sodium mercaptideprepared by the interaction of metallic sodium and a tertiary alkylmercaptan containing from 12 to 16 carbon atoms per molecule.

11. A catalyst for the polymerization of conjugated diolefins whichcomprises particles of metallic sodium having an average diameter withinthe range of from about 0.01 to about 0.02 mm. dispersed in xylenecontaining from about 0.5 to about 5.0 per cent by weight based on thesodium of a sodium mercaptide containing from about 8 to about 20 carbonatoms per molecule.

12. In a process for the polymerization of a polymerizable organiccompound in the presence of a finely divided, dispersed alkali metal aspolymerization catalyst, the improvement which comprises admixing saiddispersed alkali metal with said polymerizable compound in the form of adispersion of particles having an average diameter not greater thanabout 0.02 mm. in an inert liquid dispersing medium together with aminor amount, based on said alkali metal and not greater than 5 per centby weight thereof, of a mercaptide of an alkali metal.

13. The improvement of claim 12 in which said dispersed alkali metal issodium and is admixed with said polymerizable organic compound in anamount of 0.1 to 0.5 per cent by weight thereof and said mercaptide is asodium mercaptide of a tertiary alkyl mercaptan having between 12 and 16carbon atoms per molecule and is present in said dispersion in an amountbetween 0.5 and 5.0 per cent by weight of said dispersed sodiumcatalyst.

14. In a process for the polymerization of a conjugated diolefin in thepresence of a finely divided and dispersed alkali metal as apolymerization catalyst, the improvement which comprises using as saidcatalyst a dispersion of an alkali metal and an alkali metal mercaptidein a liquid hydrocarbon prepared as in the process of claim 12.

15. A method for the preparation of a dispersion of metallic sodium inxylene which consists of adding from 5 to 35 weight per cent metallicsodium to liquid xylene and comminuting said sodium in said xylene byvigorous agitation at 210 to 230 F. and in the presence of 0.5

to 5 weight per cent, based on the sodium, of

sodium tertiary dodecyl mercaptide, for a time suflicient to giveparticles of sodium having an average diameter of 0.01 to 0.02 mm., andcooling a resulting dispersion to below the melting point of sodium.

16. A method for the preparation of a dispersion of an alkali metal inan inert liquid bydrocarbon boiling above the melting point of saidalkali metal which consists of adding from 5 to 35 weight per cent of analkali metal to such an inert liquid hydrocarbon and comminuting saidalkali metal in said liquid hydrocarbon by vigorous agitation at atemperature above the melting point of said alkali metal and in thepresence of 0.5 to 5 weight per cent, based on said alkali metal, of amercaptide of said alkali metal having 8 to 20 carbon atoms per moleculefor a time sufiicient to give particles of said alkali metal having anaverage diameter of 0.01 to 0.02 mm., and cooling a resulting dispersionto below the melting point of said alkali metal.

17. A composition of matter consisting of liquid xylene containing 5 to35 weight per cent of sodium dispersed therein in the form of particleshaving an average diameter of 0.01 to 0.02 mm., and 0.5 to 5 weight percent, based on the sodium, of sodium tertiary dodecyl mercaptide.

18. A composition of matter consisting of a normally liquid inerthydrocarbon containing 5 to 35 weight per cent of an alkali metaldispersed therein in the form of particles having an average diameter of0.01 to 0.02 mm., and 0.05 to 5 weight per cent, based on said alkalimetal, of a mercaptide of an alkali metal containing 8 to 20 carbonatoms per molecule.

WILLIE W. CROUCH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Name Date Gotty May 22, 1917 Ebert July 30, 1940Soday Jan. 11, 1944 Tanner Oct. 15, 1946 FOREIGN PATENTS Country DateGreat Britain Jan. 30, 1930 Greatv Britain July 3, 1941 Number Number324,489 537,701

